Shallow plot

I don't understand the fascination with harems, it always makes the story feel cheap. There is not a problem with the MC being surrounded by girls if only one was a love interest and the rest were his actual friends. But almost all the time I see a harem, the girls all manage to have feelings for the MC and that becomes their entire personality. Why?

Sure Aria ended up with the Hero instead of him, but that shouldn't have broken him to the point that he felt the need to go on a journey. Its okay for him to be hurt, but after reading the flashback, my reaction was "That's it?". Why did the goddess give him her blessing, it's not like something tragic happened to him. If he went on a journey to find a true friend instead of to build a harem it'd be better.

"Its every man's dream to have a harem." Really? There's nothing wrong with a poly relationship but again, why does the mangaka think this is the solution to Wazu's problem of feeling lonely? Again, could've been better. Also not a fan of the trope where the girl instantly falls in love with the guy that saves her. Not realistic and makes her one dimensional.